PLAN DE CONTINGENCIA - VELOCIDADES MÁXIMAS EN (M/S)

VELOCIDADES MÁXIMAS EN (M/S)

D. Señalización

5.4. PLAN DE CONTINGENCIA

The project to be undertaken is a design of an iron removal pretreatment system for a small reverse osmosis (RO) unit. The iron removal system will use naturally occurring air to oxidize and precipitate dissolved iron in well water incoming to the RO unit. The precipitate will be filtered out by an

inexpensive filter. This is done in order to extend the life of the more expensive RO filter membranes.

The iron removal system will feature a flow-through design and will be mounted on an auxiliary skid near the RO unit. Restrictions include refraining from using an air pump or other device that will require additional power to operate the pretreatment system.

Figure 2: Iron-fouled RO Membrane (Membranes should be white)

Location of Work

AquaTech will be testing hard well water from a Stillwater resident to establish the initial specifications listed below. The assembly and testing of the prototype will be done in the Biosystems Lab. Initial calculations used water conditions at Pumps of Oklahoma in Oklahoma City, OK due to equipment shipping difficulties.

Description of Client

AquaTech will conduct designs and testing for Pumps of Oklahoma, Incorporated. Pumps of Oklahoma is a wholesale supplier of industrial, municipal, agricultural, and environmental pumps. They supply submersible and above ground pump equipment all over the world. Pumps of Oklahoma is located in Oklahoma City, OK and has 18 employees. Adam Avey, the team leader of AquaTech, served as the summer intern for this company in the summer of 2012 and worked to design and fabricate the current Reverse Osmosis system.

Industry Analysis Trends

Consumers in the United States pay scrupulous attention to the quality of the water they are drinking.

This is evident with the increase of bottled water consumption in the U.S., which continues to climb throughout the years.

Figure 3: Bottled Water Consumption

Many people in the U.S. are concerned about drinking water because of contaminants such as bacteria, viruses, pesticides, petroleum products, metals and metalloids, and strong acids among others.

Technologies for water treatment are becoming more effective and less costly. Recently, there has been a lot of new developments in water treatment, some of them include: activated carbon, ozonation, ultraviolet germicidal irradiation, and bioceramic water amplification, among others.

Marketing Strategy

For this particular product a great marketing strategy would be selling the Reverse Osmosis System to construction companies that could put install it in houses, that way Pumps of Oklahoma could design a standard prototype for a particular type of houses and build a whole lot of them, instead of building customized products or products that couldn’t probably fit in a particular house.

Competitive Products

The most common water treatment products that are used for well water are listed below in Table 1. Table 1: Competitive Products

Product Technique Price Range Website

Terminox ISM Chlorine injector and mixing tank

$550 - $975 www.budgetwater.com

Pyrolox Granular water

filtration media

$670 -$ 885 www.qualitywaterforless.com Greensand Glauconite greensand

filtration media

$625 - $885 www.qualitywaterforless.com

Birm Filtration media $435 - $710 www.qualitywaterforless.com

Eagle Redox Alloy Iron Oxidization Catalyst

$25 www.qualitywaterforless.com

Technical Analysis

The U.S. Environmental Protection Agency (EPA) secondary drinking water standard for iron is 0.3 parts per million. Above this level, water may develop an orange color. AquaTech researched several different methods in order to create a pretreatment that will remove ferrous iron from drinking water. A chemical analysis was conducted in order to quantify the amount of oxygen needed to oxidize the iron and filter it mechanically. Methods were examined from common household water treatment systems, large-scale wastewater aeration systems, and existing patents used for iron oxidation and removal.

Chemical Analysis

The team used the following reaction equation found in Appendix B. The team used water conditions of the Pumps of Oklahoma water well, assuming 3.2 ppm Iron, Fe, in the water.

Using Fe(II) + ¼ O2 + 2OH^- + ½ H2O Fe(OH)(s)

Given 3.2ppm Fe in tested water,

3.2mg/L Fe * mol/55.85g Fe * 1g/1000mg * ¼ mol O2/1 mol Fe * 32g O2/1 mol O2 = 0.000458 g/L O2

= 0.458 mg/L O2

= 0.459 ppm O2

Air is composed of about 21% O2. Since air has a molecular weight of about 28.96g/mol, there is about 251 mg/L of O2 available in the air. This is assuming the ideal gas law holds and that the temperature of the air is about 25^oC and at standard pressure. Therefore, there should be adequate amounts of oxygen available in the incoming air to completely oxidize the Fe(II) to Fe(OH).

Common Methodology

Water Softeners

Water softeners, which charge water with resins such as potassium chloride and sodium chloride, are commonly used to remove low levels of ferrous iron around 1 – 3 ppm. However, it is not uncommon to remove up to 10 depending on the water conditions. The pH level highly affects the oxidization process of iron, which is unwanted with the use of a water softener. Therefore, softeners increase performance with a lower pH level. However, water softeners are often expensive units ranging from $500 to over

$1000. Also, the resin must be replaced regularly, becoming an increasingly expensive task that is often done by qualified contractors. Since many water softeners work by replacing the hard metals with sodium, this can create a possible health issue. People with history of hypertension or heart risk are advised to abstain from using water softeners, since it will add a new level of salt into your daily diet.

Aeration Systems Large-scale Treatment

Many wastewater treatment plants use different aeration systems in order to achieve an adequate level of oxygen transfer required for aerobic waste treatment. Two principal types of aeration systems are diffusion-air systems and mechanical aeration. While diffusion-air aeration requires an introduction of air or pure oxygen by a submerged diffuser, mechanical aeration devices agitate the water to promote a mixture with the air from the atmosphere. Thus, mechanical aeration requires a motor and power source, but not a pumping system.

Two common types of mechanical aeration used in postaeration systems are low-speed surface aerators and submerged turbine aerators. Low-speed surface aerators are typically the most economical choice, except when high oxygen transfer rates are required. Most plants maintain two or more aerators in rectangular basins.

One of the most economical aeration systems is called cascade aeration. Cascade aeration uses the available head and a thin film of water to create turbulence as it falls over a series of steps. The most common equation used for cascade aeration was developed by Barrett in 1960:

𝐻 = 0.11𝑎𝑏(1+0.046𝑇)^𝑅−1 (English Units)

where 𝑅 = deficit ratio = ^𝐶_𝐶^𝑠^−𝐶^𝑂

𝑠−𝐶

CS = dissolved oxygen saturation concentration of the wastewater at temperature T, mg/L CO = dissolved oxygen concentration of the postaeration influent, mg/L

C = required final dissolved oxygen level after postaeration, mg/L

a = water-quality parameter equal to 0.8 for a wastewater-treatment plant effluent b = weir geometry parameter for a weir, b = 1.0; for steps, b = 1.1; for step weir, b = 1.3

10 T = water temperature, ^oC

H = height through which water falls, ft

However, this technique requires enough flow to raise DO levels and often takes up a large amount of space. For water conditions at the Pumps of Oklahoma well in Oklahoma City, OK, the team assumed that CS is 9.08 mg/L at 20 ^oC (Appendix D), CO is 0 mg/L (assume anaerobic groundwater), C is 3.6 mg/L (assuming there is a higher limit of iron, 25 mg/L), a is 0.9 due to water clarity, b is 1.0, and T is 20 ^oC.

With these inputs, the height, H, is calculated to be 3.5 feet. However, this design would require wide lateral movement as well as its height requirement. While this may be a low-cost option, the space requirement and difficulty of installation makes this an inadequate option.

Household Water Treatment

In some household iron oxidation systems, a venturi apparatus, or eductor, aerates the water so that the ferrous iron is oxidized, resulting in a ferric form. Once converted to ferric iron, the water is able to be run through a mechanical filtration unit for iron removal. In order for the system to run smoothly, the oxygen must be then removed from the water so the fluid is in a single-phase form. In order for this to occur, a deaeration technique must be applied. Although eductors are relatively expensive, the

maintenance requirements are very low, since there is no chemical or resin required to refill. However, many eductors are installed with an air compressor to ensure proper iron oxidation. Compared to water softeners, a high pH level is desired in order for an optimized oxidization rate. Little safety risk was found with the use of venturi apparatus.

Patent Searches

AquaTech found four patents that proved particularly relevant to the iron pretreatment system focusing in the aeration and deareation of water. Full patents can be found in Appendix A.

 Reactor Apparatus for Treating Water in Iron Removal System (US 5725759)

 Water Aerator and Method (US 4255360)

 Method and Apparatus for Removing Iron from Well Water (US 5080805)

 Iron Removal System and Method (US 5096580)

Reactor Apparatus for Treating Water in Iron Removal System, patent 5725759, was published in 1998 and provides a valuable method to deaerate the water before it continues past pretreatment. Water Aerator and Method, patent 4255360, was published in 1981 and gives an example of a submergible electrically powered water pump used for the aeration of water. Method and Apparatus for Removing Iron from Well Water, patent 5080805, was published in 1992 and focuses on water aeration by means of a bubbling device connected to a source of pressurized air. Iron Removal System and Method, patent 5096580, was published in 1992 and uses a venturi apparatus to mix the air and untreated water. In theory, patents 4255360 and 5725759 could be combined to convert the ferrous iron to a ferric state through aeration and then proceed to deaerate the water to form a single-phase fluid in the system.

Requirements & Specifications Customer Requirements

The details of AquaTech Engineering Solutions’ project requirements have purposely been left somewhat vague by our customer in order to prevent the limitation of creativity by previous suppositions. That being said, there are some baseline specifications that must be met:

 The device must achieve the EPA standard for acceptable iron content in drinking water.

 The device must treat the water in a continuously flowing stream.

 The device should avoid the use of additional mechanical hardware (such as a compressor).

 The device should be able to remove whatever substances (such as air) that have been added to the water stream before the stream continues on the reverse osmosis system.

 The device must stand alone on a skid separate from the RO system

Development of Quantitative Engineering Specifications

Essential quantitative data will be acquired via chemical calculations and controlled physical experimentation. The details are as follows:

AquaTech Engineering Solutions will conduct experiments to determine a well water sample’s iron oxidation potential with a given ferrous iron concentration. Experiments to quantify the ideal air to water ratio and required residence time will be performed. Establishing these two parameters will allow flow rates to be defined and for the selection of a reaction vessel, venturi, aeration nozzle, and

precipitate filter.

To determine the ideal air to water ratio, first, a theoretical chemical analysis will be performed. Bottle testing will follow to establish the physical limitations of the theoretical maximum given our particular circumstances. Bottles will be filled with certain air and water volumes and immediately mechanically agitated for a given amount of time, filtered through 5-micron paper filter and then tested for iron content. Initial physical testing values will be based upon the theoretical maximum found through chemical analysis.

Bottle testing will also be the means of determining the most appropriate residence time for maximum ferrous-to-ferric iron conversion. The most effective air to water ratio (determined previously) and mechanical agitation will preface increasing residence times. Following residence time, the sample water will be filtered through 5-micron filter paper and then tested for iron content. Results from this series of experiments and the previous will be recorded and analyzed via Microsoft Excel.

Experimentation

A lab test was researched and conducted to determine if the Hanna Instruments Iron Checker would be able to correctly calculate the amount of ferrous iron in the well sample in addition to the total amount of iron present in ppm. After the lab tests were finished, a field test was conducted on a well for real ferrous and total iron values.

Lab Test

To ensure field readings accuracy, a standard curve for ferrous iron was derived in the lab using the following reagents and procedure (Figure 2). The concentration of ferrous ammonium sulfate used was originated from Standard Methods for the Examination of Water and Wastewater (Standard, 1980). The remaining reagent concentrations were derived from a lab that was conducted at Truman State

University (Truman, 2008).

Table 2: Reagents used in making Fe(II) standards

Reagent Molecular Formula Use

Ferrous Ammonium

Sulfate 6- Hydrate Fe(NH4)(SO4)2*6H2O Known amount of ferrous iron in standard (1,10) Phenanthroline C12N2H8 Coloring Agent

Sodium Acetate NaOCOCH3 Buffering agent to fix pH

Sulfuric Acid H2SO4 Stabilizes Fe(II) and

takes care of impurities

A mass spectrophotometer sends out a pre-set wavelength of light and reads the absorbance of that light through a sample. The absorbance can be used to calculate the concentration of a substance, like iron, by Beer’s Law as seen below:

A = εbc Where A = Absorbance

ε = Molar Extinction Coefficient (L/mol*cm) b = Path length (1cm)

c = Concentration (mol/L)

Beer’s law is valid for absorbance, which is dimensionless, between 0.1 and 1.0 in which it has a linear relationship with concentration (Muller, 2000). This is used to check standard solutions. The wavelength used for iron by the Hanna Instruments Iron Checker is 525nm, so the mass spectrophotometer was also set at 525nm.

The standards were made according to the procedure below to achieve [Fe(Phen)3]²⁺. This molecule turns a bright reddish orange color and can be measured by the mass spectrophotometer (Muller, 2000).

Fe²⁺ + 3 Phen→ [Fe(Phen)3]²⁺

1. Dissolve 0.7022g of Fe(NH4)(SO4)2*6H2O and 2.5mL of sulfuric acidto 1L with deionized water.

2. In a separate 100mL volumetric flask, add 0.1g of (1,10) phenanthroline and fill to volume with deionized water (DI). Stir on stirrer until solution is clear.

3. In another 100mL volumetric flask, add 10g of sodium acetate and fill to volume with DI. Stir on stirrer until solution is clear.

4. Set out 7 100mL volumetric flasks for the 7 standards (0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0ppm) and label them accordingly.

5. In the 5.0ppm flask, add 5mL of the ferrous ammonium sulfate solution, 10mL of (1,10) phenanthroline solution, and 8mL of the sodium acetate solution. Fill to volume with DI water and allow them to set for 10 minutes before measuring their absorbance with the mass spectrophotometer.

6. For the other six standards, repeat Step 5 except add the corresponding amount of ferrous ammonium sulfate solution as the flask reads. For example, for 4ppm add 4mL of

Fe(NH4)(SO4)2*6H2O, etc.

7. Read each absorbance and record the absorbance vs. concentration at 525nm.

8. Plot absorbance vs. concentration in Excel and check linearity of the line. If R²=0.99 or better, than Beer’s Law was fulfilled.

The standards were measured and the linearity was conserved, as seen below.

Table 3: Standards and Absorption measured by mass spectrophotometer Standard Absorption

Figure 1: Plot of standard concentration of ferrous iron vs. absorption

Figure 2: Ferrous Iron Standards in the lab

Field Test

A field test was conducted at a local home in Stillwater, OK. The well tested has been tested for high concentrations of sulfate, another inorganic that makes water “hard”. A new batch of (1,10)

phenanthroline and sodium acetate was made in the lab that afternoon to take to the well site in addition to the Hanna Instruments Test Reagents for total iron content. Supplies needed for the field test were borrowed from Dr. Penn from the Plant and Soil Science department at OSU. Four well samples were tested for both total iron and ferrous iron and can be seen in Table 4. The field procedure was conducted as follows:

y = 3.5258x + 0.047

15 For ferrous iron concentration:

1. Draw 20mL of well sample and fill to the brim of the tube and seal to minimize oxidation.

2. Take 10mL of well sample and put into one cuvette (cuvette 1) to use as the zeroing agent for the Hanna Instruments Iron Checker.

3. Add 1.0mL of the pre-made (1,10) phenanthroline and 0.8mL of the pre-made sodium acetate solution to a separate 10mL cuvette (cuvette 2).

4. Fill cuvette 2 to volume with raw well sample.

5. Seal cuvettes and click the button on the Hanna Instruments Iron Checker to turn it on.

6. Place cuvette 1 in the checker and click the button again.

7. Open and place cuvette 2 in the checker and hold the button until the timer on the checker begins.

8. After two minutes, the concentration of ferrous iron will read digitally. Record the concentration and repeat.

For total iron concentration:

1. Draw 20mL of well sample and fill to the brim of the tube and seal to minimize oxidation.

2. Take 10mL of well sample and put into one cuvette to use as the zeroing agent for the Hanna Instruments Iron Checker.

3. Click the button on the checker and place the zeroing sample into the checker.

4. Click the button again.

5. Remove the cuvette and add one packet of the Hanna Instruments Test Reagents to the 10mL sample.

6. Gently swirl until the reagent is dissolved and place back into the checker.

7. Hold the button on the checker until the timer begins.

8. Record concentration reading after two minutes and repeat with a new sample.

Table 4: Field test results

Sample Ferrous Iron

(ppm) Total Iron

Figure 4: Adam and David Prepare Well Sample Figure 5: Deep Water Well Used for Testing

Development of Quantitative Engineering Specifications

Essential quantitative data will be acquired via chemical calculations and controlled physical experimentation. The details are as follows:

precipitate filter.

Design Concepts

After the team’s review of several iron removal systems listed in the Technical Analysis, the following two designs were developed. Both options were designed in order to minimize power and space requirements in order to prove suitable as a household unit.

Aeration via misting nozzles

This design option receives the influent directly from the well and passes it through an eductor. The eductor draws air into the stream, creating a turbulent, two-phase flow. AquaTech employee and

In document FACULTAD DE INGENIERÍA ESCUELA ACADÉMICO PROFESIONAL DE INGENIERÍA CIVIL “Diseño hidráulico del canal L-02 Huabal, en el distrito de Mórrope, Lambayeque – 2018” (página 113-121)